Percussion tool bits, or hammers tools, are commonly used in the construction/demolition/quarry industry. Tool bits having various striking faces, for example, blunt, moil, or chisel striking faces, are chosen for a particular application. Blunt tool bits, which have a flat striking face, are particularly useful for breaking up rocks in quarries. Moils or chisels, which have a generally pointed striking face, may be used in quarries to break up a large rock into smaller pieces or for trenching.
These tool bits can be quite large, typically having a shank diameter of 5-81/2 inches and a weight of many hundreds of pounds or more. As such, they are generally used in connection with a hydraulic hammer that is boom mounted. These tools are quite costly, often starting at $1000.00 or more.
The prior art hammer tool 2, as shown in FIG. 1, typically includes an elongated cylindrical body 4 having a shank portion 6 at one end of body 4 and a forward portion 8 at the other end of the body 4. At the distal end 10 of the forward portion 8 is an integral striking face 12 (a blunt face is shown). The shank portion 6 of the hammer tool 2 is received into a chuck housing (not shown) of a power hammer 14, (which is shown in phantom). Much of the body 4, including the forward portion 8 and the striking face 12, extends externally and downwardly of the power hammer 14, below a lower chuck housing face 16. In use, the power hammer is raised and lowered over a work surface (not shown) in order to bring the striking face into striking contact with the work surface, typically in a force range from 800-15,000 foot pounds (depending on the hammer class).
As shown in FIG. 1, the shank portion 6 and the forward portion 8 have a substantially uniform diameter d.sub.pa along a longitudinal length L.sub.opa of the entire tool. Below lower chuck housing face 16, the diameter of the tool d is uniform along the overall longitudinal length of the forward tool portion L.sub.pa, which is the longitudinal length of the forward tool portion to the distal end 10. Thus, the portion of the hammer tool extending below the power hammer has to be of a length relative to the diameter of the tool to impart a sufficient force, determined essentially by the hammer manufacturer and force class.
When new, the tool bit is at its maximum longitudinal length. During use, the longitudinal length slightly decreases. Also during use, the length of the tool bit extending below the hammer can tend to flex during rough handling. Such flexing can generate small stress fractures, of which can lead to ultimate catastrophic failure. Ultimate catastrophic failures often occur within the first 24 hours of use of a new tool bit.
An objective of the present invention is to maintain or increase the life of these expensive tool bits by decreasing the length of the tool that extends below the hammer, yet still provide the same or more striking mass.